The present invention relates to fluorescence detectors and, more particularly, to such detectors in which the sample is disposed in a tube, such as a capillary tube.
As discussed in "Fluorescence Analysis of Picloliter Samples," Edmund A. Claude, Mroz and Lechene, Analytical Biochemistry 102, 90-96 (1980), biochemical analysis of very small samples--on the order of picoliters--is required in both basic and applied sciences of cell biology. As explained, many attempts to analyze such samples have been tried, and many of these attempts have used microfluorescence methods. These methods have limitations, however, in the compounds that can be analyzed and the ease with which assays can be performed. The apparatus disclosed in the above-referenced article includes a fluorometer chamber, created optically by using a capillary tube as a flow-through cell, and a microscope-fluorometer to excite fluorescence in and to record fluorescence from the fluorometer chamber within the capillary. Excitation radiation is directed transverse to the capillary tube and fluorescent radiation is similarly collected transverse to the capillary tube.
Such an apparatus has inherent problems in that the excitation radiation is not effeciently delivered to the sample volume since it is directed transverse to the capillary tube and, consequently, passes through only a small portion of the sample volume. Similarly, the fluorescent radiation cannot be efficiently collected and delivered to a detector. The cumulative loss of excitation and fluorescent radiation results in an instrument having greatly reduced sensitivity. Further, such devices cannot accurately of efficiently measure the absorbance characteristics of liquid samples.
It is further desired that fluorescence detectors have provisions for reaction and sample blanking, sample blanking being the signal representing the sample's detection background.
It is also desirous that such a detector be reliable and have low manufacturing costs.